1. Field of the Invention
The present invention relates to an x-ray diagnosing apparatus in which x-rays which are radiated from an x-ray source and transmitted through an object to be examined are converted into an optical image by an image intensifier, and the optical image is input to a TV camera to display a fluoroscopic image on a TV monitor, or the optical image is used to perform photography by using an x-ray film.
2. Description of the Related Art
In general, a C- or U-shaped arm type holding unit is used in an x-ray diagnosing apparatus for angiography of an object to be examined. For example, a C arm type holding unit is designed such that an x-ray tube is fixed to one end of a C-shaped C arm, and an image intensifier (to be referred to as an I.I. hereinafter) is fixed to the other end of the C arm to oppose the x-ray tube. The I.I. is used to convert x-rays, radiated from the x-ray tube and transmitted through an object to be examined, into an optical image. Note that other arm type holding units having shapes other than C and U shapes are sometimes used. When angiography of the object is to be performed, the x-ray tube and the I.I. arranged on the two ends of the C arm of the holding unit must be set at proper angles with respect to a portion, of the object, to be subjected to fluoroscopy (or a portion to be photographed).
In angiography of an object, first, second, and third axes which are defined in advance are used. These axes are perpendicular to each other. The first axis is the body axis indicating the direction of the head and lower limbs of the object. The first axis is generally called the X axis. The second axis is an axis which is perpendicular to the body axis and indicates the direction of the width of the shoulders. The second axis is generally called the Y axis. The third axis is a vertical axis which is perpendicular to the body axis and passes through the isocenter. The third axis is generally called the Z axis. Of these axes, the Z axis is used as a reference, and the other two axes are adjusted with respect to the Z axis to perform angle setting operations in photography. More specifically, the C arm of the holding unit is rotated about the X axis as a rotation center to be set at an angle .beta. (arm rotational angle .beta.), and is rotated about the Y axis as a rotation center to be set at an angle .alpha. (slide angle .alpha.). These angle setting operations are performed by an angle setting section. These set angles are stored in a memory. Therefore, when the second and subsequent photographing operations are to be performed, the photographing angle data is read out from the memory to reproduce the previous photographing direction.
In photography of blood vessels of the object with a contrast medium, diagnostic angles which are clinically defined are used independently of angles associated with the holding unit (to be referred to as mechanical angles hereinafter), such as the slide angle .alpha. and the arm rotational angles .beta.. Diagnostic angle .theta. and .eta. are defined as follows:
.theta.=LAO/RAO PA1 .eta.=CRA/CAU
where LAO and RAO correspond to the arm rotational angle .beta.. More specifically, LAO is a counterclockwise rotational angle of the arm rotational angle .beta., and RAO is a clockwise rotational angle of the arm rotational angle .beta.. In addition, CRA is an abbreviation for "cranial"; and CAU, "caudal". CRA and CAU correspond to the slide angle .alpha.. More specifically, CRA is a rotational angle of the slide angle .beta. in the direction of the head, and CAU is a rotational angle of the slide angle .beta. in the direction of the lower limbs.
While diagnostic and mechanical angles coincide with each other, the slide angle .alpha. is identical to the diagnostic angle .eta., and the rotational angle .beta. is ideotical to the diagnostic angle .theta.. This state is displayed on a display unit.
According to a recent 3-axis control type holding unit, a rotating operation with the Z axis being set as a reference can be performed, in addition to rotating operations with the X and Y axes being set as references. If used, an angle setting operation can be quickly performed to locate the arm at the optimal position with respect to an object to be examined. This, for example, facilitates a tracking operation with respect to a blood vessel.
FIG. 1 is a front view showing an x-ray diagnosing apparatus including a 3-axis control type holding unit. A 3-axis control type holding unit 10 includes a column (Z axis) rotation axis 30 for setting a column rotational angle .gamma. as a mechanical angle, a spindle (Y axis) rotation axis 32 for setting an arm rotational angle .beta. as a mechanical angle, and an (X axis) slide axis 34 for setting a slide angle .alpha. as a mechanical angle. The slide angle .alpha., the arm rotational angle .beta., and the column rotational angle .gamma. can be set by a controller (not shown).
While the column rotational angle y is set to be 0, a C arm 16 is positioned at the head and abdomen of an object 200 to be examined. If a state "A" shown in FIG. 1 is set, a slide angle .alpha..sub.1 coincides with a diagnostic angle .eta., and an arm rotational angle .beta..sub.1 coincides with a diagnostic angle .theta..
If, however, the column rotational angle .gamma. is set to be 90.degree. to position the C arm 16 at the lower limbs of the object 200, i.e., if a state "B" in FIG. 1 is set, a slide member 16B is moved on the slide axis 34, and the spindle (Y axis) rotation axis 32 is also rotated. As a result, the slide angle .alpha. and the arm rotational angle .beta. are changed from the initial angles. That is, since the number of axes (degrees of freedom) of the 3-axis control type holding unit 10 is larger than that of a 2-axis control type holding unit by one, a slide angle .alpha..sub.3 and an arm rotational angle .beta..sub.3 do not coincide with the diagnostic angles .eta. and .theta., respectively.
In addition, this inaccurate diagnostic angle .theta. is stored in a memory. For this reason, even if the diagnostic angle is read out from the memory, in a rephotographing operation, to be used for positioning for photography, the previous photographing direction cannot be reproduced. Under the circumstances, it takes much time to reproduce an accurate angle setting operation, resulting in an increase in operation load of an operator. Furthermore, changes in column rotational angle .gamma. cause rotation of an image. Such inconvenience can be eliminated, i.e., the image can be corrected, by also rotating a TV camera attached to an I.I. 20. However, since a film changer 22 and a cinematic camera are mounted on the I.I. 20 together with the TV camera, a mechanism for rotating these components is required. As a result, the apparatus is complicated.